Because of its reactivity with so many types of materials, carbon monoxide is widely used in the chemical industry. One particularly important use for CO is in the manufacture of phosgene which is widely used for the manufacture of isocyanates. Phosgene is made commercially by reaction of CO and chlorine gas over a catalyst such as activated charcoal, as follows: EQU CO + Cl.sub.2 .sub.cat. COCl.sub.2.
In carrying out this reaction, it is essential that the gas be of the highest purity, particularly with respect to non-condensible impurities which make recovery of the CO more difficult. Thus, hydrogen and hydrocarbons must be essentially completely excluded lest they form HCl, which is non-condensible. Carbon monoxide is, of course, usually made in commercial quantities by processes in which the CO is accompanied by substantial quantities of such impurities. Of the impurities which are most commonly contained in CO-containing gases (CO.sub.2, H.sub.2, O.sub.2, N.sub.2 and CH.sub.4), it is most difficult to remove H.sub.2 and CH.sub.4 and thus to obtain quite high purity CO.